@Speechley could a minimum term discount have ended? you would have been told at signup when this would end, sky don't currently send reminders
you would need to contact sky and negotiate lower price, if you receive an offer you find acceptable you must accept it there and then as you wont get the same offer next time you call, in return you will need to commit to a new 18 month minimum term contract
this link may also help
https://www.sky.com/help/articles/been-overcharged
We obviously can't see your bills. Compare it to a previous one to see where it differs. It usually involves roaming charges, sending chargeable picture messages, calls to non-inclusive numbers or a discount ending.